Compact laser disks provide a convenient method for storing high density digital data. A single optical disk at a standard size of 51/4 diameter can store up to 600 megabytes of information. This is equivalent to over 30 reels of magnetic tape or to 10 of the most advanced Winchester storage disks. An important advantage of optical disks is therefore their high data storage density.
A further advantage of optical disks is that they are read with a non-contacting read head, this contrasts with read heads used on conventional, magnetic storage devices. Since there are no mechanical connections to the disk during the read cycle, the optical disk has a greatly extended lifetime compared to magnetic storage devices. Optical disks are therefore virtually immune to wear and are protected from physical damage through contact when read. Typically, the layer of the optical disk which stores information is embedded within a thin layer of plastic or glass that protects it from dust or wear problems.
Another advantage of optical disks is that they are considerably more accessible than magnetic tape storage devices. Data stored on optical disks can be accessed far more quickly than data stored on conventional, magnetic data storage devices. Further, optical disks are portable and are more reliable than tapes or floppy disks.
Unfortunately, conventional laser disks have a major disadvantage. Conventional laser disks cannot be easily erased and rerecorded. This disadvantage makes them unusable for many mass data storage applications. Various schemes have recently been proposed for providing erasable, compact laser disks. It appears that at least some of these proposals rely on heating the disk to allow for erasure and rerecording. Such heating will always have a finite, detrimental effect on disk reusability and lifetime.
A need therefore exists for an erasable and reusable compact laser disk that is capable of providing high density storage and that is neither stressed nor physically manipulated when reused.